A problem arises when it is desired to widely distribute a mass produced device having text entry capabilities in a number of countries having different languages and writing styles and written symbols, as it is not cost-effective to modify the device to accommodate each local language and style of writing. This is particularly true for the case of mobile stations, also referred to as cellular telephones and wireless terminals, that very typically include a conventional-looking numeric keypad of the type found on touch tone telephones. Associated with the numeric keys 2, 3, 4, etc., are the characters ABC, DEF, GHI, etc, as is well known.
It is also well known to enter text using such a keypad. One technique relies on multiple depressions of a certain key to scroll through a limited set of letters, those displayed on the key, and to select a particular letter for entry when the key depressions terminate. For example, after entering an alphanumeric text mode of operation depressing the numeric key 2 one time displays the letter A, depressing the numeric key again displays a B, depressing it again displays a C, depressing it again displays the associated number 2, and depressing it again once more displays the letter A (the scrolling wraps around to the start of the sequence). Pausing after a depression for some period of time, such as for about a second, causes the currently displayed character to be entered onto a text stream being composed by the user. The zero 0 key can be used to enter a space between letters, numbers and words.
While well suited for use with those languages that employ the Latin alphabet, this conventional technique can prove to be limiting when attempting to enter other types of alphabetic symbols associated with other languages, which can have more complex rules relating to the relationships between the constituent parts of the written language, such as vowels, consonants and special characters and modifiers. Hindi is one such language.
As such, to enter a language such as Hindi a significant problem arises when one desires to employ a device capable of text entry, such as a cellular telephone, that is provided only with a simple 12 key numeric-type of keypad.
ISCII (IS 13194:1991 Indian Script Code for Information Interchange) specifies an alphabetic code that can be used for encoding multiple Indian national languages with a single codeset. ISCII has been used as the basis for the Indian script code point allocation in Unicode (Devanagari, in particular, is allocated in U+0900-U+097F in Unicode). In its annex D, the standard specifies an INSCRIPT keyboard for a PC environment.
INSCRIPT specifies a phonetic PC keyboard for Indian languages. Similarly to the general design of ISCII, the INSCRIPT keyboard is designed to work as a solution for multiple Indian languages. It provides a phonetic mapping of the keyboard that is readily usable across the Indian languages, even though they use distinct scripts for the writing of the language.
The words of the Indian language are typed in and stored in the strict phonetic order, even if the phonetic order may not always correspond to the visual appearance of the displayed text.
The INSCRIPT keyboard requires two distinct keys for each pair of independent and dependent vowels. The INSCRIPT also requires the explicit use of virama (vowel killer) to produce consonant clusters. As maybe appreciated, this approach does not lend itself for implementation on a limited keypad type of user input device, such as an ITU-T keypad of a type that is typically found in a cellular telephone.